This invention relates in general to a device for cleaning fusers for electrographic reproduction apparatus, and more particularly to a reproduction apparatus fuser cleaning web and a cleaning web advancement and control mechanism.
In typical commercial electrographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser assembly, utilized in typical reproduction apparatus, includes at least one heated roller and at least one pressure roller in nip relation with the heated roller. The fuser assembly rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
With fuser assemblies of the above described type, it has been found that there is a tendency of a portion of the marking particles in an image to adhere to the pressure roller rather than remaining with the receiver member during the fusing operation. This is referred to as image offset. Thereafter the offset marking particles can transfer back to subsequent receiver members being fused to form undesirable image artifacts such as ghost images for example. Also, the offset marking particles may transfer to the fuser roller when no receiver member is present therebetween and then to the back-side of subsequent receiver members to form undesirable marks thereon. In order to minimize this image offset effect, an offset preventing oil is applied to the rollers of the fuser assembly. The offset preventing oil has a viscosity which, lowers the surface energy of the rollers and makes it less likely that marking particles will adhere thereto.
Since the offset preventing oil is not one hundred percent efficient in preventing image offset, and because the offset preventing oil itself can cause some image artifact problems during fusing, it has been found desirable to provide a mechanism for cleaning the fuser rollers of residual marking particles and excess offset preventing oil. One general type of cleaning mechanism used in reproduction apparatus includes a web cleaner. For example a typical web cleaner is shown in U.S. Pat. No. 4,853,741, issued Aug. 1, 1989, in the name of Ku, for cleaning photoconductive webs. The web cleaner has a roll of cloth material that runs from a supply roll to a take-up roll and is in contact with the surface to be cleaned (e.g., photoconductive web, fuser roller or pressure roller of a fuser assembly, or a transfer roller). After a predetermined number of reproductions have been made, the cloth material web is advanced a few degrees to the take-up roll to provide a clean web surface in contact with the surface to be cleaned. It has, however, been found that there is difficulty in precisely controlling the amount of web material that is periodically advanced so that the web roll may be most efficiently used and the need for replacement of the web roll is minimized.
In view of the above, this invention is directed to a mechanism for cleaning the surface of an operative element of a reproduction apparatus. The cleaning mechanism includes an elongated web of cleaning cloth material. A first support provides a supply of the elongated web of cleaning cloth material, and a second support provides a take-up for the elongated web of cleaning cloth material. A motor is operatively coupled to the second support to drive the second support for selectively advancing of the elongated web of cleaning cloth material from the first support to the second support to provide a clean portion of the elongated web of cleaning cloth material to clean the operative element. An encoder, associated with the motor, produces a string of pulses while the motor is operative to drive the second support. A logic and control unit produces a signal for turning the motor on for a period of time establishing a web advancement cycle where a given predetermined number of pulses in a pulse string are produced by the encoder. Responsive to the actual number of pulses in the pulse string of an advancement cycle, the period of time that the motor is turned on in a subsequent advancement cycle is adjusted based on the actual number of pulses in a previous string of pulses in order to adjust advancement of the web to provide for the most efficient use of the web of cleaning cloth material.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.